1. Field of the Invention
The present invention relates to an antitheft label which can be affixed to an article of merchandise to detect merchandise that is shoplifted from a store and to thereby prevent theft.
2. Description of the Related Art
It has heretofore been known that a monitor label can be affixed to merchandise to prevent shoplifting.
Generally, when a label affixed to merchandise enters a label detection zone (a zone developed by an electric, electromagnetic or magnetic field having a certain magnitude) formed by transmitting antennae installed at the doorway of a store, a specific signal is generated which is then detected by a receiving antenna installed in the same location as the transmitting antennae to thereby sound an alarm.
In one such system, an alternating magnetic field is applied to a high permeability magnetic thin ribbon or a magnetic wire. This generates in the detection zone a disturbance in the magnetic field or an output pulse having a harmonic component which is then detected. In another system, a label comprising a combination of a coil made of aluminum foil and a capacitor made of an aluminum foil is employed. When an electric field is externally applied, the label resonates and this resonance is hen detected.
Among these systems, a label employing a amorphous magnetic wire having Large Barkhausen Jump is advantageous in that it can form a system which operates at high sensitivity with little misdetection (U.S. Pat. Nos. 4,660,025, 4,686,516, and 4,797,658).
Further, JP-A-4-195384 (The term "JP-A" as used herein means an "Unexamined Japanese Patent Publication") discloses a magnetic marker utilizing Large Barkhausen Jump comprising a amorphous magnetic wire including another magnetic material having a smaller coercive force which this disposed on the ends of the magnetic wire. In this arrangement, a magnetic marker having a small size such that a pulse-generating magnetic wire alone would not exhibit Large Barkhausen Jump is said to provide good Large Barkhausen Jump. Furthermore, the magnetic marker can be miniaturized to an entire length of about 60 mm if a magnetic wire having a diameter of 120 .mu.m is used.
Such a magnetic marker is used as an antitheft label. Heretofore, such a label has comprised a detection member such as the foregoing high permeability magnetic thin ribbon (a member which generates a specific signal when subjected to a magnetic, electric or electromagnetic field), laminated with at least two tape basis. In general, one of the two tape bases is disposed on the side of the label affixed to an article of merchandise (herein after referred to-as a "sticking side") and the other tape base disposed opposite the former tape base on the label surface side (hereinafter referred to as "surface side"). The detection member is interposed between the two base tapes.
A film or paper is used as the sticking side tape base. The surface side tape base is usually used a transparent or semi-transparent film, or a white or colored paper on which price, notice, etc. are optionally printed.
Furthermore, in order to laminate the detection member with these tape bases, one of the sticking side tape base and the surface side tape base has an adhesive layer on the side thereof with which the detection member is laminated (laminated side). moreover, the sticking side tape base has an adhesive layer so that it can be affixed to merchandise.
The magnetic marker (antitheft label) disclosed in the above cited JP-A-4-195384 comprises a magnetic wire having Large Barkhausen Jump and magnetic thin ribbons (magnetic sheet) having a smaller coercive force Hc than the magnetic wire attached to both ends of the magnetic wire. However, the Large Barkhausen Jump of the magnetic marker can easily change depending on the contact condition of the magnetic wire with the magnetic thin ribbon. The magnetic marker loses its Large Barkhausen Jump or exhibits unstable diamagnetism over time or the actual working conditions. Therefore, the magnetic marker is disadvantageous in that it varies widely in its properties as an antitheft label. For example, if there is a gap between the magnetic wire and the magnetic thin ribbon or if the surface of the magnetic thin ribbon or magnetic wire is not smooth, then there is insufficient contact between the two components. These conditions give rise to unstable Large Barkhausen Jump. Similarly, if the antitheft label is affixed to articles having various curvatures, the magnetic wire and the magnetic thin ribbon are not in fixed contact with one another, thus giving rise to unstable Large Barkhausen Jump.
The term "instability in Large Barkhausen Jump" as used herein means a defect in the BH loop such as process of magnetization which deteriorates the Large Barkhausen Jump. The results in the drawing of a minor loop, an extreme rise in the critical field (hereinafter referred to as "H*") and the generation of jitter (an irregular loop disturbance).
Such instability in Large Barkhausen Jump markedly deteriorates the detectability of the antitheft label by a detection system.
For example, if the label no longer exhibits Large Barkhausen Jump, the pulse voltage output or the harmonics generated by the label is reduced. If H* rises, it is difficult to detect the antitheft label in a small exciting magnetic field. Furthermore, if jitter is generated, it is difficult to distinguish the signal of the antitheft label from noise. In any case, the detection sensitivity is lowered or the zone of the detection zone is decreased.
Furthermore, if a transparent film or white paper as usual is used as the surface side tape base, it is disadvantageous in that the detection member can be easily recognized when the label is affixed to merchandise. Once the detection member is recognized, one can know that the label is an antitheft label. This means that if a shoplifter peels the label off the merchandise or locates other merchandise free of such a label, it becomes easy to shoplift. In other words, such a label affixed to merchandise is unlikely to fulfill its antitheft function.
In order to solve these problems, a semi-transparent film may be used as the surface side tape base instead of a transparent film. However, even a semi-transparent film cannot fully hide the detection member. Furthermore, such a semi-transparent film is a special film which adds to the cost of the label.
Furthermore, the thickness of a paper, if a paper is used as the surface side tape base, may be increased. However, the increasing in the thickness of the paper not only adds to the cost but also the volume of the label. The increase in the volume of the label impairs the operating efficiency of the labelling machine or restricts the kind of merchandise to which the label can be affixed.
The use of a colored paper may be proposed. However, the color of such a colored paper which can hide the member to be detected may be limited, for example, to blue. On the other hand, the label can form a striking contrast with some colors of the merchandise to which it is affixed. Furthermore, if the color of the surface side tape base is limited, the various needs of retail stores cannot be met.
On the other hand, if a label including a sticking side tape base comprising a film or paper which has heretofore been used is affixed to transparent merchandise or the like, it is disadvantageous in that the detection member can be recognized when viewed from the sticking side of the label through the merchandise.
Furthermore, JP-A-7-140898 discloses an antitheft label comprising a display support (a surface side tape base) having on the side thereof opposed to a protective element (laminated side) a layer having a transparency which is low enough to prevent the protective element from being recognized with respect to visible light rays. The low transparency layer of JP-A-7-140898 is an opaque color sheet.
However, the use of the opaque color sheet as an extra component not only added to the cost, but also the thickness of the entire label. The increase in the thickness of the label may impair the operating efficiency of the labelling machine.